Thanks I'll look for 7s.Ive just bought a 200b to part out. Can I use the fuse box out of that ? Maybe I should steal some other wiring, relay etc ?

Nah the 120y has 7 " lights,cause thats what i was getting the Liteace lights for. It has melted the fuse box through the extra current, but I'm going to put a b310 fuse box in there, which seems to be a better plastic.

Now I'm really concerned about melting something. Believe me if it can go wrong , then it WILL go wrong for me ! The 120y lights are 5 and a quarter or 5 and three quarters or something. It's got an L series motor so I don't know what difference that makes.
Thanks for all the info . I hope it helps some others aswell.
I don't know how everyone else drives around with candles for headlights!.

I bought the smaller Hellas in the 200B from a wrecker. Good value too.
Aparently they were used in some Statesman & Fairlane models.

P.S.
I have been keeping an eye open for some 7" QH's in wreckers, but haven't seen any yet. Even Rush's didn't have any when I was there last.

Why pay $100 for Hella H4 when you can recycle some from the same wrecker you got the wiring loom. Most 7" round headlighted commercial vehicles have h4 inserts, my favourite is the Toyota Liteace. For the people with Square headlights (late Sunnys) Navara's or Nissan Praries/Pulsars usually have them too.
Then it's just some aftermarket globes. Stupid Cheap used to have 80/100's which i always went for, always wanted that little extra on low beam. They don't seem to carry them any
more, the fools.

Here's the Hella link.
Click on the 'Auxiliary Lighting' tab, then scroll down to Headlamp Conversion Kits.

These babies are probably about as good as you will find, but don't come cheap.
The Narva ones would probably come a close second & at a fair saving in cost too.

A Hella H4 100w conversion kit used to be about $100 Trade,
3 of my 1000's have them now, I didn't bother with fitting relays, and had no stress, although it would be a good idea...
makes a huge improvement from the sealed beams..

here is a Narva link as i couldnt see them on the Hella website..

yeah pretty much what they cost from repco, 30 bucks each, and globes were like 22 bucks or somethin, the wire and relays came from work and took stuff all time to wire up.

my 7" H4 lights cost me $55 for the pair for Mark Gibbs Panel House in Slacks Creek, they are glass not plastic. plus bulbs

According to my original 120Y owners manual, the headlights in these cars were rated at 50/40 when they left the showroom, but lord only knows whats in there now.

If we assume a 'nominal' 12.5 volts in the electrical system, then the lights draw a paltry 4 amps each & there's two of them, so there's a nominal 8 amps flowing through the switch for the headlights.

Now Datsun engineers are not fools, they know that using wiring & switchgear that handles much more than this is only going to cost more money, so the system is engineered to safely handle the current draw needed by a stock lighting system, but not much more.

Next, we switch to the QH lights with the standard 55/60 bulbs. The current draw is now only 4.8 amps per light with a new total of 9.6 amps. Doesn't look like a lot more, but it represents a 20% increase in current flow.
The system would handle this just fine when the car was new, but after 30 years many electrical connections have developed a little corrosion & the electrical resistance may not let all the current reach the headlights. The end result is less than satisfactory performance & sometimes a switch or fuse connestion that gets a bit hot.
Many people, like me, don't mind a further upgrade to 100/90 bulbs & the resulting 16 amp draw is going to send the lighting system into a [metaphoric] meltdown.

The recomended fix is the relays, but for the store bloke to say that the current draw is the same shows a lack of understanding of both the subject, & of 30 year old cars from the low cost end of the market.

Just make sure that the bulbs get all the current they need, & make sure they have a good earth & as I have said before, even those standard QH lights will really light up your life.

Oh yeah, check the voltage across the battery terminals with the engine running at about 2,000 rpm & headlights on. You are looking for more than 14 volts. If it's down, then have your regulator checked [if you have an adjustable regulator] to ensure that the system is running at full rated voltage. That should brighten things up.